Phosphonic diesters are esters of phosphonic acid [HP(O)(OH)2], which is tautomeric with phosphorous acid [P(OH)3]. The phosphonic diesters are frequently also referred to, not entirely correctly, as secondary phosphites. However, the true derivatives of phosphorous acid are only the triesters.
Diphosphonic diesters are the diesters of diphosphonic acid:(HO)(O)PH—O—PH(O)(OH),formerly also referred to as diphosphorous acid.
(Cf. in this regard Römpp Lexikon der Chemie, Georg Thieme Verlag, Stuttgart, N.Y., 1990, “Phosphites”, “Phosphonates”, “Phosphonic acid”, “Diethyl phosphite”, and “Dimethyl phosphite”.)
Silane-functional, water-free, thermally curable mixtures, particularly coating materials, which can crosslink by polycondensation via the silane groups are known from international patent application WO 2004/072189 A2 or European patent applications EP 0 267 689 A2 and EP 1 193 278 A1.
The known silane-functional, water-free, thermally curable mixtures comprise optionally amine-blocked acidic phosphoric esters, optionally amine-blocked sulfonic acids, organotin compounds, such as dibutyltin dilaurate, dibutyltin diacetate, tin octoate or dibutyltin oxide, amines, such as triethylamine, tetramethylguanidine or triethylenediamine, and compounds of titanium, of tin(II), of zinc or of bismuth as thermal curing catalysts.
Each of these catalysts, however, has specific drawbacks.
Thus the strongly acidic catalysts exhibit the undesired phenomenon of severe interactions with customary, known light stabilizers of the kind used in thermally curable mixtures, particularly coating materials. Furthermore, they may lower the storage stability of the known silane-functional, water-free, thermally curable mixtures to such an extent that the mixtures gel prematurely.
The metal catalysts and the amine catalysts lead frequently to instances of yellowing, which manifests itself interferingly in the case in particular of clearcoats produced from the known silane-functional, water-free, thermally curable mixtures.